Apparatus for pneumatically grinding divided substances



y 8, 1965 E. FELD ETAL 3,184,168

APPARATUS FOR PNEUMATICALLY GRINDING DIVIDED SUBSTANCES Filed Oct. 16, 1962 INVENTORS ER/CH FEL 0 HORST PA TZER WERNER KlE/IVLEl/V BY United States Patent 9 cream. (31. z41 39 The present invention provides an apparatus for pneumatically grinding divided substances, for example granular, gritty or coarsely powdered dry substances, in a grinding apparatus with the help of grinding air.

The apparatus of the invention is particularly applicable to pharmaceutic products and organic or inorganic dyestuli pigments.

In accordance with the invention, dust particles are prevented from depositing on the Walls of the passage of flow within the grinding apparatus, thereby avoiding obstruction of the grinding apparatus which would require the latter to be stopped after a short Working time, for example a few minutes, in order to be cleaned. The apparatus of the invention thus has the advantage of permitting continuous working.

As synthetic materials which can be used for making the coverings, there enter into consideration all those which are sufiiciently elastic, for example rubber or rub berlike substances such as chloroprene and its polymers.

It is known from the field of flow technique to cover the walls of apparatus which use no pressure in a simple manner wit-h rubberlike sheets. This mode of construction is not appropriate, however, for the apparatus of the present invention as in the interior of the grinding chambers of jet mills pressures are produced by centrifugal forces and the pressure necessary for conveying the dustgas stream leaving the grinding apparatus, which pressures would press the sheets against the walls and thus render their surfaces immovable and stiff as is the case with metal surfaces, so that the product could not be prevented from caking on the walls.

The apparatus of the present invention is constructed in the manner wherein the inner sides of the covers of the mill case, that is those surfaces of the covers which face the grinding space, are provided with coverings of elastic synthetic material which are secured along their edges to the covers so that a hollow space is formed between the elastic synthetic material and the covers. The apparatus of the invention furthermore comprises members for introducing compressed air into the hollow space and discharging it therefrom so that the coverings of synthetic material are kept in rhythmical motion. The compressed air is introduced and discharged through these members with the help of a periodic control member.

In another mode of construction of the apparatus of the invention, the hollow space is subdivided into several cells of the same or different dimensions, all of which or part of which may be connected one to the other by channels. For this purpose, the covering of synthetic material is fastened to the covers in several places, for example, by adhesive.

The apparatus of the invention may also be constructed in a manner such that the inner sides of the covers are provided with flat bodies of elastic synthetic material which contain hollow spaces. The individual hollow spaces may be of different dimensions and may all or in part be connected to one another by channels.

An apparatus suitable for use in carrying out the process of this invention is illustrated diagrammatically by way of example in the accompanying drawing.

3,184,,lh Patented May 18, 1965 "ice Referring to the drawing which is a vertical section, 400 cubic meters (measured at N.T.P.) per hour of grinding air are introduced at 1 into ring channel 2 under an initial pressure of, for example, 3 atmospheres gage and are then discharged from there, for example, at the velocity of sound, through jet nozzles 3 into the grinding space. Flowing along the periphery of the grinding space, the grinding air then rotates about the axis of the grinding space, owing to the approximately tangential position of the nozzle channels. The latter are all arranged in the same direction.

Through short feed pipe 4, the material to be ground enters the discharge range of the nozzles and is ground in that range while being continuously rotated until a desired fineness of grinding has been obtained. The said introduction of the material to be ground is realized with the help of a small amount of conveying air which under the conditions prevailing in the present case amounts to about cubic meters per hour (measured at N.T.P.). The feed pipe is tilted in the direction of rotation (in a plane perpendicular to the plane of the drawing). The stream of air finally travels in a spiral line to the upper end of short discharge pipe 4a.

The apparatus of the invention has the effect of a wind sitter. Only the finely ground material is entrained and discharged from the grinding apparatus through short discharge pipe 4a. The discharged finely ground material is subsequently freed from the conveying air and bunkered or filled in containers.

At the top and the bottom, the mill case is closed by covers 5 and 6, respectively, screwed to ring channel 2. The lower side of cover 5 and the upper side of cover 6 are provided each with sheets 7 and 8, respectively, made of soft elastic synthetic material. Sheets 7 and 8 may be fastened to the covers, for example, by adhesive. They are provided with channels 9 which are disposed in the form of rings around the axis of the mill and are all connected one to the other by individual small channels 19. Compressed air is introduced at 11 and 12., respectively, through pipe connections. The compressed air is supplied and discharged through these pipe connections with the help of a periodic control member in a manner such that the pressure in the channels rises from 0 to 3 atmospheres gage and drops again to 0. It is not necessary that the rhythm at the upper cover and the rhythm at the lower cover be synchronous. In this manner, continuous breathing of the inner sides of the mill is obtained. Breathing is most pronounced in the range of the large ring channels and takes place, for example, 3 times a minute.

The wall thicknesses and channel widths of the covering of synthetic material may vary to obtain different effects in different places of the mill.

We claim:

I. An apparatus for pneumatically grinding divided substances comprising a grinding apparatus having a grinding chamber and means to inject a grinding fluid under pressure around the periphery of said grinding chamber, wherein the covers of the grinding chamber are provided, at the sides which face the grinding chamber, with coverings of elastic synthetic material which are secured along their edges to the covers so that a hollow space is formed between the elastic synthetic material and the covers, and members are disposed for introducing compressed air into the hollow space and discharging it therefrom to produce a rhythmical motion of the coverings of synthetic material.

2. The apparatus of claim 1 wherein the coverings are secured to the covers in several places in a manner such that the hollow space is subdivided into several cells of which at least two are connected one to the other by channels.

3. The apparatus of claim 1 wherein the covers are provided with flat elastic bodies of synthetic material containing hollow spaces.

4. The apparatus of claim 3 wherein the hollow spaces are of ditferent dimensions, at least two hollow spaces being connected one to the other by channels.

5. Apparatus for pneumatically grinding divided substances comprising a grinding chamber with top and bottom covers, means for injecting a grinding fluid under pressure around the periphery of said chamber, means for introducing material to be ground to said chamber, means for removing ground material from said chamber, a lining of an elastic synthetic material on the surfaces of said covers facing said chamber, said lining forming at least one space between the chamber and the cover, and means for introducing a compressed fluid into said space and discharging it therefrom to produce rhythmical motion in said lining.

6. Grinding apparatus as defined in claim 5 wherein said lining is secured to said cover adjacent the edges said lining has a plurality of 4, thereof and said space is formed between said lining and said cover.

7. Grinding apparatus as defined in claim 5 wherein said lining is secured to said cover at a plurality of places to form a plurality of intercommunicating spaces between said lining and said cover.

8. Grinding apparatus as defined in claim 5 wherein intercommunicating spaces therein.

9. Grinding apparatus as defined in claim 8 wherein saidispaces are of difierent sizes.

References Cited by the Examiner UNITED STATES PATENTS 2,352,327 a 6/44 Kirn 146253 2,588,945 3/52 Trost 2415 X 2,983,453 5/61 Bourguet et al. 2415 X 3,062,459 11/62 Dearing 2415 X J. SPENCER 'OVERHOLSVER, Primary Examiner. 

1. AN APPARATUS FOR PNEUMATICALLY GRINDING DIVIDED SUBSTANCES COMPRISING A GRINDING APPARATUS HAVING A GRINDING CHAMBER AND MEANS TO INJECT A GRINDING FLUID UNDER PRESSURE AROUND THE PERIPHERY OF SAID GRINDING CHAMBER, WHEREIN THE COVERS OF THE GRINDING CHAMBER ARE PROVIDED, AT THE SIDES WHICH FACE THE GRINDING CHAMBER, WITH COVERINGS OF ELASTIC SYNTHETIC MATERIAL WHICH ARE SECURED ALONG THEIR EDGES TO THE COVERS SO THAT A HOLLOW SPACE IS FORM BETWEEN THE ELASTIC SYNTHETIC MATERIAL AND THE COVERS, AND MEMBERS ARE DISPOSED FOR INTRODUCING COMPRESSED AIR INTO HOLLOW SPACE AND DISCHARGING IT THEREFROM TO PRODUCE RHYTHMICAL MOTION OF THE COVERINGS OF SYNTHETIC MATERIAL. 